Self-assembly in the classic sense refers to the autonomous and spontaneous organization of molecules and/or artificial components into patterned and well-organized structures without human or machine intervention. In other words, self-assembly spontaneously and autonomously creates patterned or structured substances with a remarkable order out of largely disordered components. From physical point-of-view, self-assembly process can be classified in two main kinds of “static self-assembly” and “dynamic self-assembly”.
Static self-assmbly refers to processes involving systems that are already at or are approaching global or at least local equilibrium without energy dissipation and there is no pre-existing patterns prior to self-assembly occurs. In this form of self-assembly, the fabrication of ordered structures may need some sort of external energy e.g. stirring; though, once the process is accomplished, the self-assembled structure is stable and cannot be adjusted or reconfigured, unless a different equilibrium state is reached as a result of changing environment. Formation of molecular crystals and protein crystals, stable surfactant-free self-assembly of micelle-like nanostructures, supramolecular self-assembly of single- and multi-walled tubes, DNA-guided self-assembly of single- and multi-component nanostructures, synthesis of self-assembled nanostructured proteins for therapeutic purposes, and self-assembly of block copolymers into giant polymer vesicles, are exemplary of static self-assembly. In contrast, in dynamic self-assembly the process occurs outside of the thermodynamic equilibrium (i.e.
out-of-equilibrium) and the formation of patterns and structures only occurs if the system is dissipating energy, e.g. in form of heat.
In this category, ordered structures are formed out of pre-existing non-ordered patterns and structures through input of energy delivered either chemically or by an external energy source, and this energy dissipates. For instance, formation of patterns in reaction-diffusion systems, self-assembly of millimeter-sized magnetic discs, controlled self-assembly in microfluidic systems, fabrication of two and three-dimensional arrays of magnetic colloidal crystals, self-assembly of crystalline microstructures through capillary forces, formation of electronic devices and circuits, DNA templating, and any living organism are examples of dynamic self-assembly.